Various methods and gauges have been provided in the prior art for accurately measuring or determining the effective open area of vane assemblies, for example in the various stages of turbojet engines and the like.
These gauges have been concerned with the classification or measurement of such values in connection with individual vane elements or vane clusters including a plurality of guide vanes, turbine blades and/or other similar structures. For example, U.S. Pat. No. 3,464,119 issued September 2, 1969 to Griggs disclosed a precision classification gauge for classifying individual guide vanes or the like for turbojet engines in order to facilitate assembly of various stages of the engine according to predetermined values for the effective open areas of the individual vanes.
U.S. Pat. No. 3,959,886, issued June 1, 1976 also to Griggs, disclosed a similar classification gauge adapted for classifying or determining the relative effective open area for vane clusters rather than individual vane elements.
U.S. Pat. No. 4,024,646, issued May 24, 1977 again to Griggs, disclosed yet another apparatus for simultaneously gauging and aligning movable elements of guide vane assemblies including a plurality of vanes or air foil elements in order to both classify and adjust the effective open area for the vane assembly.
U.S. Pat. No. 4,374,459, issued February 22, 1983 to Burton disclosed another classification instrument for accurately measuring both blocked and/or open flow area for air foil or vane elements such as turbine stator vanes. The last noted patent was assigned to the assignee of the present invention while the other patents noted above were also of related interest to the assignee of the present invention.
U.S. Pat. No. 4,322,887, issued April 6, 1982 to Burton, disclosed yet another method and apparatus for open flow area classification, this patent also being assigned to the assignee of the present invention.
Substantial background information is set forth by the above noted patents and reference may be had to those patents for a more complete understanding of certain aspects of the present invention. Generally, it has been found important to precisely classify or measure the effective open area for individual guide vanes or for adjacent guide vanes in a cluster or assembly. This opening is also commonly referred to as the "throat" for the individual guide vanes or guide vane assemblies and, as noted above, is critically important in connection with various stages in machinery such as turbojet engines in order to assure proper performance.
U.S. Pat. No. 3,115,711, issued December 31, 1963 to Plante, disclosed yet another classification or comparison gauge adapted for use in the same manner as those of the preceding patents.
The classification gauges disclosed by the above noted patents have been found to be suitable for classifying or measuring the effective open area of individual guide vanes, vane clusters and even complete arrays of vanes or similar structures. Generally, the above noted classification gauges function to accurately position within a precision jig one portion of an air foil or vane, such as its trailing edge, portions of the vane then being contacted by multiple mechanical probes or fingers in order to classify or measure the effective open area for that vane either alone or in combination with an additional vane or vanes in a cluster.
U.S. Pat. No. 3,327,495, issued February 4, 1982 to Plante, disclosed a staging fixture for holding a single vane nozzle assembly while providing reference surfaces corresponding to surfaces provided by "ideal vanes" in order to provide an assessment of effective open area for the single vane. To the extent that the idealized surfaces provided by the fixture correspond to surfaces for additional vanes in a cluster with the one vane, a single vane arranged within such a fixture is assumed to form a throat or effective open area in the same manner as a pair of adjacent vanes according to the present invention. Accordingly, a single vane arranged within such a fixture to effectively form a throat or effective open area is also included within the context of the present invention where reference is made to adjacent vanes.
The open flow area or effective open area for a pair of vanes is established as the width or open dimension between the adjacent vanes multiplied by the effective radial length of the opening or throat between the vanes. The radial length of the throat or opening between the vanes is determined by the spacing between the buttresses or corresponding end surfaces for the throat between the two adjacent vane elements.
Furthermore, it is important to understand that the traditional values of such a vane element, including its trailing edge location, convex air foil surface, etc., are important in determining the effective open flow area as discussed above. In addition, it has been found that other factors including air foil rotation, air foil displacement and air foil twist may further affect these open area values.
In this regard, air foil rotation refers to the angular relationship between the air foil vane element and its respective buttresses or flanges. Rotation of the air foil in either a clockwise or counterclockwise direction upon the supporting buttresses results in modification of the effective open flow area values for the vane or a vane cluster including that vane.
Similarly, air foil displacement refers to the location of the air foil or vane element upon its respective buttresses. Air foil displacement is particularly concerned with relative positioning of the air foil or vane element upon its respective buttresses in a direction perpendicular to the path of air flow passed or through the individual vanes or vane assemblies.
Air flow twist refers to relative rotation between opposite ends of the individual air foil or vane elements. Relative rotation may arise, for example, during manufacturing of the vane element with buttresses formed at opposite ends of the vane or air foil. More commonly, relative rotation may be produced between the opposite ends of the vane element when its buttresses are secured in a vane assembly, for example, a stage of a turbojet engine. If the base surfaces of the opposite buttresses are not precisely aligned or if the vane surfaces to which the buttresses are attached are not properly aligned, twisting or relative rotation between the opposite ends of the vane element may result, especially at high temperatures and/or under stresses developed within the engine.
The preceding discussion is typical of other variations in vane elements which may vary their effective open area in a vane cluster. In any event, such variations further demonstrate the need for precisely measuring the effective open area for such vane elements. The gauges provided by the patents discussed above have been found effective in that regard. However, because of the large numbers of vanes or vane clusters requiring such analysis, there has been found to remain a need for a further improved method and apparatus for measuring their effective open area.
In the prior art designs discussed above, a unique tool or device was needed for each variation of vanes. Accordingly, there was also found to remain a need for a more universal, adjustable tool or scanning gauge, particularly for use in engine development and the like, where vane sizes and shapes may be changed during development while facilitating the measurement of an effective open area in vane clusters including those vanes.